Waksman — 142 — Actinomycetes 



After moistening of the air-dried soil, the ratio of actinomycetes to 

 the total numbers of microorganisms, determined by plate counts, de- 

 clined as the bacterial numbers increased. This was followed by an 

 increase in the ratio of actinomycetes due to a decrease in the num- 

 bers of bacteria, until a nearly constant ratio of 20 to 25 per cent of num- 

 bers of actinomycetes to total colonies was established. When soil was 

 heated to 65° for 1 hour, the ratio of actinomycetes to total numbers of 

 colonies on the agar plate changed from an initial 30 per cent to 15 per 

 cent. After 2 weeks, only 3 per cent of the colonies were those of ac- 

 tinomycetes. This was followed by an increase in the relative numbers 

 of actinomycetes. However, even 4 months after treatment the ratio of 

 actinomycetes to total numbers was only one-fourth the ratio before 

 treatment. 



Specific nature of soil actinomycetes.— O^ the four genera of the 

 Actinomycetales, three are represented abundantly in the soil. A large 

 number of species belonging to all these genera have been isolated and 

 described. The aerial mycelium producing Streptowyces species are the 

 most common; these are followed by the Nocardia types. The Micro- 

 monosfora group is also well represented in the soil; several forms have 

 been isolated and described, but because of their slower growth on the 

 common media under the usual conditions of cultivation, only few spe- 

 cies have so far been recognized. They are particularly abundant in 

 high-temperature composts and in lake bottoms. Thermophilic actino- 

 mycetes are particularly abundant in soils receiving stable manures 

 (459). 



The anaerobic group, that is, the members of the genus Actinomyces, 

 have so far not been reported isolated from the soil. Although they are 

 brought into the soil in the diseased bodies of animals, it is not known 

 to what extent they are able to survive there. It is recognized, for ex- 

 ample, that certain pasture lands are apparently favorable to infection 

 with lumpy-jaw of grazing cattle. This would seem to point to the 

 presence of A. hovis in the soil, at least under certain conditions. Be- 

 cause of the need for special methods of isolating and cultivating these 

 organisms, no attempt has ever been made to isolate them directly from 

 the soil. During a survey of the microbial population of peat bogs 

 (473), an organism belonging to the anaerobic group was isolated from 

 a Florida peat. It grew only under anaerobic conditions and at a tem- 

 perature above 40 °C. It was definitely a species of Actinomyces, but, 

 unfortunately, no further study was made of this culture. 



Many actinomycetes have been isolated from the soil and have been 

 described as distinct species. Certain others have been recognized, but 

 have been described not as species but rather as group species, since the 

 overlapping among various strains makes it rather difficult to establish 

 species types. Without a sufficiently clear diflFerentiation, on the one 

 hand, between certain actinomyces-like organisms and true bacteria, 

 and, on the other, between different genera, especially Nocardia and 



